This project involves the utilization of measurements of concentrations of diuretic in biologic fluids--blood and urine-as a probe of disease states. The pharmacodynamics of furosemide have been characterized in a group of normal subjects and it has been demonstrated that measures of drugs in urine closely correlate to response. Preliminary studies in patients with congestive heart failure demonstrate that in this disease state, the response to the diuretic is decreased; the dose-response curve is shifted downward and to the right. Further studies will probe other disease states and attempt to assess the mechanism (s) of the shift in the curve.